On the Mac anyway...
This has worked for a few...
Make a New Location, Using network locations in Mac OS X ...
System Preferences>Network, top of window>Locations>Edit Locations, little plus icon, give it a name.
System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.
The interface that connects to the Internet should be dragged to the top of the list.
Instead of joining your Network from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.
For 10.5/10.6, System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...
Also, turn off IPv6:
System Preferences » Network » AirPort » TCP/IP tab » Configure IPv6
Or whatever Interface you use.
See if the Disk is issuing any S.M.A.R.T errors in Disk Utility...
Open Activity Monitor in Applications>Utilities, select All Processes & sort on CPU%, any indications there?
How much RAM & free space do you have also, click on the Memory & Disk Usage Tabs.
Open Console in Utilities & see if there are any clues or repeating messages when this happens.
In the Memory tab, are there a lot of Pageouts?
I checked all of your suggestions and took screenshots of the Activity Monitor since I really don't understand it all . Then tried some videos, with the same SLOW loading. Then I opened System Prefferences, Looked at Flash & Flip4Mac settings, changed a few things (can't remember what) and now videos load ZIPPY!!!
Thank you again. I couldn't have done it without YOU:)